1. Field of the Invention
The present invention relates to a socket for an electrical part that is used for burn-in test of an electrical part (e.g. an IC (Integrated Circuit) package), more particularly, relates to a socket for an electrical part used for an IC package of an LGA (Land Grid Array) type or BGA (Ball Grid Array) type.
2. Description of the Prior Art
Conventionally, the socket for an electrical part is known as a tool used in the processing for preventing the initial failure of an IC package (e.g. burn-in test).
Among the sockets for the electrical parts, the socket for an electrical part used in the burn-in test or other kinds of tests of the LGA type IC packages or the BGA type IC packages is constituted so as to be able to electrically connect the plural electrodes formed on the reverse surface of the IC package to an external electrical test circuit when the IC package is accommodated on the predetermined position of the socket body.
In addition, such socket for an electrical part comprises contact pins which are arranged so as to correspond with the electrodes of the IC package in one-to-one. For this, the contact pin holding holes corresponding to the pitch and the configuration state of the electrodes of the IC package are formed in the socket body in which contact pins are accommodated.
FIGS. 13A to 13E show the configuration for holding the contact pins 101 of such socket for the electrical part 100 (see Japanese Patent laid-Open Publication No. 2004-342466).
As shown in FIGS. 13A to 13E, the holding member 102 of the contact pins 101, which are a part of the socket body, are constituted by stacking three holding plates (i.e. first to third holding plates) 103-105, and, for inserting the contact pins 101, the holes 106-108 are formed so as to pass through the three holding plates 103-105 along the Z-axis direction (i.e. vertical direction). The holding plate 104 which lies midway among the three holding plates 103-105 (i.e. the second holding plate), is constituted so as to be able to move slidably against other two holding plates (i.e. the first holding plates 103 and the third holding plate 105), and so the holes 107 of the second holding plate 104 can be shifted against the holes 106 of the first holding plate 103 and the holes 108 of the third holding plate 105 (see FIGS. 13A to 13C).
According to such configuration of the contact pin 101, the holding member 102 receives the under terminals of the contact pins 101 under the state that the positions of the holes 106-108 of the three holding plates 103-105 correspond each other. When the engagement concave portions 110 formed at the lower side of the contact pins 101 moves inside the holes 106-108 to a position corresponding to the second holding plate 104 (see FIGS. 13D and 13E), the second holding plate 104 is moved slidably against the first and third holding plates 103 and 105, and is inserted into the engagement concave potions 110 (see FIGS. 13A to 13C). As a result, the inner surfaces of the holes 107 of the second holding plate 104 press the contact pins 101 against the inner surfaces of the holes 106 and 108 of the first and second holding plates 103 and 105. Therefore, the contact pins 101 are restrained from moving along the axis line direction of the holes 106-108 of the first to third holding plate 103-105 (i.e. z-axis direction), and additionally, rotational movement in the holes 106-108 of the first to third holding plate 103-105 (i.e. rotational movement along the X-Y plane) can be restricted. Consequently, the contact pins 101 are held by the first to third holding plate 103-105.
As shown in FIGS. 13A through 13E, according to the conventional socket 100 for the electrical part, the tips (i.e. lower terminal) of the contact pins 101 are projecting out from the lower surface of the first holding plate 103 constituting the socket body, and the tips of the contact pins 101 are engaged into the engagement holes of a substrate having an external electrical test circuit (not shown in Figures).
However, when such conventional socket 100 for the electrical part is mounted on the device employing the system to electrically connect the contact pins 101 and the external electrical test circuit by pressing the tips of the contact pins against the electrical terminals on the substrate, the tips of the contact pins 101 are deformed by the forces of screw clamps between socket body (which contains the first to third holding plate 103-105) and the substrate. Such deformation causes loose connections between the contact pins 101 and the substrate, and so may cause a bad electrical contact between the contact pins 101 and the external electrical test circuit.